Research will continue on the binding and metabolism of steroid hormones in the CNS, including studies with dispersed neurons in tissue culture. Electron microscopy, lanthanum tracer and freeze fracture techniques will be used to study membranes of gametes, supporting cells, and preimplantation embryos at various stages of development. Granulosa cell metabolism and hormone binding will be studied in tissue culture and Leydig cell function will be studied from testicular preparations. Electron Probe studies on the external and internal ionic environment of the blastocyst will continue. Steroid-protein interaction and the role of P-450 in aromatization will be investigated. BIBLIOGRAPHIC REFERENCES: Davies, I.J., J. Siu, F. Naftolin and K.J. Ryan. Cytoplamic binding of steroids in brain tissues and pituitary, In Raspe, G. (ed.), Advances in the Biosciences, Vol. 14, Pergamon Press/Vieweg, Oxford, 1975. Davies, I.J., F. Naftolin, K.J. Ryan and J. Siu. Estradiol receptors in the pituitary and anterior hypothalamus of the rat: measurement by agar gel electrophoresis. Steroids 25: 591-609, 1975.